Follow these steps carefully to build layers of flavor, resulting in a perfectly cooked, robust lentil filling. The key is to allow the aromatics and spices to develop before adding the liquids.

1. Sauté the Aromatics: Heat the olive oil in a large skillet, Dutch oven, or heavy-bottomed pot over medium heat. Once the oil is shimmering, add the finely diced yellow onion. Sauté for 5-7 minutes, stirring occasionally, until the onion becomes translucent and soft. This initial step is crucial for building a sweet and savory base. Add the minced garlic and cook for another minute until fragrant, being careful not to let it burn.
2. Cook the Vegetables: Add the finely diced carrot and red bell pepper to the skillet with the onions and garlic. Continue to cook for another 5-7 minutes, stirring periodically. The goal is for the vegetables to soften and release their natural sweetness, further deepening the flavor profile of the dish.
3. Bloom the Spices: Add the ground cumin, ground coriander, turmeric powder, smoked paprika, and optional cayenne pepper directly into the skillet with the vegetables. Stir constantly for about 60 seconds. This process, known as “blooming,” toasts the spices in the hot oil, which unlocks their essential oils and makes their flavors significantly more potent and aromatic.
4. Cook the Lentils: Pour in the rinsed brown or green lentils and the 4 cups of vegetable broth. Stir everything together to ensure the lentils are fully submerged. Increase the heat to high and bring the mixture to a boil.
5. Simmer to Perfection: Once the broth is boiling, reduce the heat to low, cover the skillet with a lid, and let it simmer. Cook for 25-35 minutes, or until the lentils are tender and have absorbed most of the liquid. The exact time will depend on the specific type and age of your lentils. Check them periodically after the 25-minute mark to prevent them from becoming overly soft. The ideal texture is tender but with a slight bite.
6. Wilt the Spinach: Once the lentils are cooked to your liking, remove the skillet from the heat. Stir in the roughly chopped fresh spinach. The residual heat from the lentil mixture will be more than enough to wilt the spinach perfectly in just a minute or two.
7. Final Seasoning: Taste the lentil filling and season generously with salt and freshly ground black pepper. This is a critical step to make all the individual flavors pop. Don’t be shy with the seasoning.
8. Prepare the Yogurt Sauce: While the lentils are simmering, prepare the sauce. In a small bowl, combine the Greek yogurt, fresh lemon juice, and finely chopped dill or mint. If using, add the grated garlic. Stir until everything is well-combined and smooth. Set aside in the refrigerator until you are ready to assemble the wraps.
9. Assemble the Wraps: Warm your tortillas according to the package directions. This makes them more pliable and prevents them from tearing. Lay a warm tortilla flat and spoon a generous amount of the spiced lentil and veggie filling onto the center. Drizzle with the cooling yogurt sauce. Fold in the sides of the tortilla, then roll it up tightly from the bottom to create a secure wrap. Slice in half and serve immediately.